c++ - 如何在 OpenGL 中叠加文本

Question

我目前有一个程序显示多个旋转立方体接近近平面。我想做的一件事是在屏幕的左下角显示一些文本。每当我尝试实现文本时，我的原始代码都不会显示。相反，我有一个只有文本的黑屏。我想我在推送和弹出矩阵时可能会遇到一些问题，但我无法弄清楚我在哪里搞砸了。在第 158 行使用函数 drawString 调用我的文本。

drawString("Why aren't the cubes being displayed?");

如果将其注释掉，我的原始代码将完美执行，旋转立方体不断飞向屏幕。

下面是我的全部代码。

#include <windows.h>        
#include <gl/glut.h>
#include <gl/GL.h>
#include <ctime>
#include <math.h>

#define PI 3.14159265
#define CUBES 15

GLfloat angle[CUBES] = {0.0};   

GLfloat fovy = 60.0;
GLfloat zNear = 0.0;
GLfloat zFar = 100.0;

GLfloat transX[CUBES];          //array for translated positions
GLfloat transY[CUBES];
GLfloat transZ[CUBES];

GLfloat red[CUBES];             //keep track of randomized colors
GLfloat blue[CUBES];            
GLfloat green[CUBES];

GLfloat spin[CUBES];            //spin speeds for each cube

GLfloat ambred = 1.0;           //ambient light color variables
GLfloat ambgreen = 1.0;
GLfloat ambblue = 1.0;

GLfloat lx = -10.0;             //light position variables
GLfloat ly = 0.0;
GLfloat lz = 1.0;
GLfloat lw = 0.0;




/***    drawing text on screen  ***/        //not working yet

void drawString(char *string){
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();             //save
    glLoadIdentity();           //and clear
    gluOrtho2D(0, 1024, 0, 720);
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    glColor3f(1, 0, 0); // red font

    glDisable( GL_DEPTH_TEST ); //disable depth test so renders on top

    glRasterPos2i(10, 10);
    void *font = GLUT_BITMAP_HELVETICA_18; 
    for (char* c=string; *c != '\0'; c++) {
        glutBitmapCharacter(font, *c); 
    }

        glEnable (GL_DEPTH_TEST);     //turn depth test back on

    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();  
}




/***  Creates random spin for blocks ***/
void initializeSpin(){
    for(int i=0;i<CUBES;i++){
        spin[i]= (float)rand()/((float)RAND_MAX/2.5);
    }
}

/***    Creates Random Location on Far Plane    ***/
void reset(GLfloat &x, GLfloat &y, GLfloat &z) {
    x = rand() % 101 - 50;
    y = rand() % 101 - 50;
    z = -95.0;
}

/***    Create Random Colors    ***/
void initializeColor(GLfloat &x, GLfloat &y, GLfloat &z) {
    x = (float)((rand()%10)*0.1);   
    y = (float)((rand()%10)*0.1);   
    z = (float)((rand()%10)*0.1);   
}


/***    Create the Cube     ***/
void cube (int n) {
    GLfloat calcThetaY;             
    GLfloat calcThetaX;
    calcThetaY = abs (atan(transY[n]/transZ[n]) * 180 / PI);        //thetas to determine if within viewing volume
    calcThetaX = abs (atan(transX[n]/transZ[n]) * 180 / PI);
    if((calcThetaY > (fovy/2)+10) || (calcThetaX > (fovy/2)+10) || transZ[n] > zNear+10){   //added +10 to clear perspective
        reset(transX[n], transY[n], transZ[n]);             //randomize location
        initializeColor(red[n], green[n], blue[n]);             //randomize color
        spin[n]= (float)rand()/((float)RAND_MAX/2.5);       //randomize spin
    }

    glPushMatrix(); 

        glTranslatef(transX[n], transY[n], transZ[n]);
        glRotatef(angle[n], 1.0, 0.0, 0.0); //rotate on the x axis
        glRotatef(angle[n], 0.0, 1.0, 0.0); //rotate on the y axis
        glRotatef(angle[n], 0.0, 0.0, 1.0); //rotate on the z axis

        glColor3f(red[n], green[n], blue[n]);                       //color of cube

        glutSolidCube(2);                           //draw the cube

    glPopMatrix();  




}

void myInit (void) {
    glEnable(GL_COLOR_MATERIAL);
    glEnable (GL_DEPTH_TEST);           //enable the depth testing
    glEnable (GL_LIGHTING);             //enable the lighting
    glEnable (GL_LIGHT0);               //enable LIGHT0, our Diffuse Light
    glEnable (GL_LIGHT1);               //enable LIGHT1, our Ambient Light
    glShadeModel (GL_SMOOTH);           //set the shader to smooth shader

    for(int i=0;i<CUBES;i++){
        reset(transX[i], transY[i], transZ[i]);
    }

    for(int i=0;i<CUBES;i++){
        initializeColor(red[i], green[i], blue[i]);
    }   

    initializeSpin();
}

void display (void) {
    glClearColor (0.0,0.0,0.0,1.0);                                 //black background
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);            //clear the color buffer and the depth buffer
    glLoadIdentity();  
    GLfloat AmbientLight[] = {ambred, ambgreen, ambblue};           //set AmbientLight[]
    glLightfv (GL_LIGHT1, GL_AMBIENT, AmbientLight);                //change the light accordingly
    GLfloat LightPosition[] = {lx, ly, lz, lw};                     //set LightPosition
    glLightfv (GL_LIGHT0, GL_POSITION, LightPosition);              //change LightPosition
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);        //camera position, x,y,z, looking at x,y,z, Up Positions of the camera

    for(int j=0;j<CUBES;j++){
        cube(j);
        angle[j]+= spin[j];         //speed of rotation
        transZ[j]+=0.25;            //speed of travel through Z-axis    
    }


    drawString("Why aren't the cubes being displayed?");


    glutSwapBuffers(); 
}

void reshape (int w, int h) {
    glViewport (0, 0, (GLsizei)w, (GLsizei)h); 
    glMatrixMode (GL_PROJECTION); 
    glLoadIdentity ();
    gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);       //set the perspective (angle of sight, width, height, , depth)
    glMatrixMode (GL_MODELVIEW); 
}

void quitProgram (unsigned char key, int x, int y) {
    if(key == 113) exit(0);
}

int main (int argc, char **argv) {
    srand(time(NULL));
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_DEPTH);             //set the display to Double buffer, with depth
    glutInitWindowSize(500, 500);                               
    glutInitWindowPosition(100, 100);                           
    glutCreateWindow ("boxes2"); 
    myInit(); 
    glutDisplayFunc (display); 
    glutIdleFunc (display); 
    glutReshapeFunc(reshape); 
    glutKeyboardFunc(quitProgram); 
    glutMainLoop(); 
    return 0;
}

Answer 1

您忘记禁用照明:

/***    drawing text on screen  ***/     
void drawString(char *string)
{
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();             
    glLoadIdentity();   
    int w = glutGet( GLUT_WINDOW_WIDTH );
    int h = glutGet( GLUT_WINDOW_HEIGHT );
    glOrtho( 0, w, 0, h, -1, 1 );

    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    glDisable( GL_DEPTH_TEST ); 

    glDisable( GL_LIGHTING );
    glColor3f(1, 0, 0);

    glRasterPos2i(20, 20);
    void *font = GLUT_BITMAP_HELVETICA_18; 
    for (char* c=string; *c != '\0'; c++) 
    {
        glutBitmapCharacter(font, *c); 
    }

    glEnable( GL_LIGHTING );

    glEnable (GL_DEPTH_TEST);     

    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();  
}

在上下文中:

#include <GL/glut.h>
#include <ctime>
#include <cmath>

#define PI 3.14159265
#define CUBES 15

GLfloat angle[CUBES] = {0.0};   

GLfloat fovy = 60.0;
GLfloat zNear = 0.0;
GLfloat zFar = 100.0;

GLfloat transX[CUBES];       
GLfloat transY[CUBES];
GLfloat transZ[CUBES];

GLfloat red[CUBES];          
GLfloat blue[CUBES];         
GLfloat green[CUBES];

GLfloat spin[CUBES];         

GLfloat ambred = 1.0;        
GLfloat ambgreen = 1.0;
GLfloat ambblue = 1.0;

GLfloat lx = -10.0;          
GLfloat ly = 0.0;
GLfloat lz = 1.0;
GLfloat lw = 0.0;

/***    drawing text on screen  ***/     
void drawString(char *string)
{
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();             
    glLoadIdentity();   
    int w = glutGet( GLUT_WINDOW_WIDTH );
    int h = glutGet( GLUT_WINDOW_HEIGHT );
    glOrtho( 0, w, 0, h, -1, 1 );

    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    glDisable( GL_DEPTH_TEST ); 

    glDisable( GL_LIGHTING );
    glColor3f(1, 0, 0);

    glRasterPos2i(20, 20);
    void *font = GLUT_BITMAP_HELVETICA_18; 
    for (char* c=string; *c != '\0'; c++) 
    {
        glutBitmapCharacter(font, *c); 
    }

    glEnable( GL_LIGHTING );

    glEnable (GL_DEPTH_TEST);     

    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();  
}

/***  Creates random spin for blocks ***/
void initializeSpin()
{
    for(int i=0;i<CUBES;i++)
    {
        spin[i]= (float)rand()/((float)RAND_MAX/2.5);
    }
}

/***    Creates Random Location on Far Plane    ***/
void reset(GLfloat &x, GLfloat &y, GLfloat &z)
{
    x = rand() % 101 - 50;
    y = rand() % 101 - 50;
    z = -95.0;
}

/***    Create Random Colors    ***/
void initializeColor(GLfloat &x, GLfloat &y, GLfloat &z)
{
    x = (float)((rand()%10)*0.1);   
    y = (float)((rand()%10)*0.1);   
    z = (float)((rand()%10)*0.1);   
}

/***    Create the Cube     ***/
void cube (int n)
{
    GLfloat calcThetaY;             
    GLfloat calcThetaX;
    calcThetaY = abs (atan(transY[n]/transZ[n]) * 180 / PI);        
    calcThetaX = abs (atan(transX[n]/transZ[n]) * 180 / PI);
    if((calcThetaY > (fovy/2)+10) || (calcThetaX > (fovy/2)+10) || transZ[n] > zNear+10)
    {
        reset(transX[n], transY[n], transZ[n]);            
        initializeColor(red[n], green[n], blue[n]);        
        spin[n]= (float)rand()/((float)RAND_MAX/2.5);      
    }

    glPushMatrix(); 

    glTranslatef(transX[n], transY[n], transZ[n]);
    glRotatef(angle[n], 1.0, 0.0, 0.0); 
    glRotatef(angle[n], 0.0, 1.0, 0.0); 
    glRotatef(angle[n], 0.0, 0.0, 1.0); 

    glColor3f(red[n], green[n], blue[n]);   

    glutSolidCube(2);                       

    glPopMatrix();  
}

void myInit (void)
{
    glEnable(GL_COLOR_MATERIAL);
    glEnable (GL_DEPTH_TEST);         
    glEnable (GL_LIGHTING);           
    glEnable (GL_LIGHT0);             
    glEnable (GL_LIGHT1);             
    glShadeModel (GL_SMOOTH);         

    for(int i=0;i<CUBES;i++)
    {
        reset(transX[i], transY[i], transZ[i]);
    }

    for(int i=0;i<CUBES;i++)
    {
        initializeColor(red[i], green[i], blue[i]);
    }   

    initializeSpin();
}

void display (void) 
{
    glClearColor (0.0,0.0,0.0,1.0);                                
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    

    glMatrixMode (GL_PROJECTION); 
    glLoadIdentity ();
    double w = glutGet( GLUT_WINDOW_WIDTH );
    double h = glutGet( GLUT_WINDOW_HEIGHT );
    gluPerspective (60, w / h, 1.0, 100.0);  

    glMatrixMode (GL_MODELVIEW); 
    glLoadIdentity();  

    GLfloat AmbientLight[] = {ambred, ambgreen, ambblue};          
    glLightfv (GL_LIGHT1, GL_AMBIENT, AmbientLight);               
    GLfloat LightPosition[] = {lx, ly, lz, lw};                    
    glLightfv (GL_LIGHT0, GL_POSITION, LightPosition);             
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);       

    for(int j=0;j<CUBES;j++)
    {
        cube(j);
        angle[j]+= spin[j];         
        transZ[j]+=0.25;            
    }

    drawString("Why aren't the cubes being displayed?");

    glutSwapBuffers(); 
}

void quitProgram (unsigned char key, int x, int y)
{
    if(key == 113) exit(0);
}

int main (int argc, char **argv) 
{
    srand(time(NULL));
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);            
    glutInitWindowSize(500, 500);                              
    glutInitWindowPosition(100, 100);                          
    glutCreateWindow ("boxes2"); 
    myInit(); 
    glutDisplayFunc (display); 
    glutIdleFunc (display); 
    glutKeyboardFunc(quitProgram); 
    glutMainLoop(); 
    return 0;
}